1. Field of the Invention
The present invention relates to a technical field regarding a data recording apparatus exposing a data recording medium to light to record information, and particularly, to a data recording apparatus capable of controlling the intensity of light appropriately.
2. Description of the Related Art
In recent years, when a data recording medium (i.e. DVD-RW) in which data can be recorded/erased is exposed to laser light to carry out recording, two methods are employed for keeping the intensity of laser light constant. One of them is a method in which the temperature change of a laser diode emitting laser light is detected to supply an amount of current depending on the temperature change. The other is a method in which a front monitor for detecting the intensity of laser light is provided, and a detection signal from the front monitor is peak-held to perform control so that the peak value is kept constant.
In the former method, however, the emission efficiency of the laser diode that varies with the temperature is represented by typical values, and open control based on the typical value is performed. As a result, the variations in the characteristics of the laser diode are directly reflected as variations in the control of light intensity, thereby reducing the accuracy of light intensity. Particularly, it is one of the most crucial topics in the case of high-speed recording where light intensity has a significant influence on recording characteristics.
The above-discussed other method does not reduce the accuracy of light intensity because the peak hold capability can be used to perform feedback control. However, the circuit for peak hold has a large scale.
The object of the present invention is to provide a data recording apparatus, which is capable of accurately controlling the intensity of light applied to a data recording medium, and which can be manufactured at low costs because the circuit is made small.
The above object of present invention can be achieved by a data recording apparatus of the present invention. The apparatus is provided with: a photoirradiation device for applying light to a data recording medium to record data; a detection device for detecting the intensity of light emitted from the photoirradiation device; a lowpass filter for receiving a signal which is outputted from the detection device; a switch device for keeping the lowpass filter in the operating state during the time period over which a signal having a predetermined time duration is recorded; a sampling device for sampling a signal which is outputted from the lowpass filter; and a control device for controlling the intensity of light emitted from the photoirradiation device based on the signal sampled by the sampling device.
According to this data recording apparatus, the lowpass filter is made to go into operation during the time period over which a signal having a predetermined time duration is recorded, whereby the output signal outputted from the detection device can be extracted in predetermined timing related to the data, which is recorded in the data recording medium, to be provided for the lowpass filter.
Accordingly, only a detection signal reflecting light intensity correctly can be taken, for example, by extracting a portion of consecutive record marks, thus making it possible to accurately control the intensity of light emitted from the photoirradiation device. Also, according to this data recording apparatus, circuits for peak-holding and the like are not required, and therefore the scale of the circuit can be reduced, thus making it possible to reduce the costs associated with assembling the device.
In one aspect of the present invention, the data recording medium associated with the data recording apparatus is a rewritable recording medium in which recorded data is erased by the light emitted from the photoirradiation device, and the photoirradiation device records new data while erasing data recorded in the data recording medium.
In this case, the output signal outputted from the lowpass filter for erasing recorded data may be equal in level to the output signal outputted from the lowpass filter for recording new information. However, according to this data recording apparatus, the intensity of light emitted from the photoirradiation device can be reliably reflected in the output signal outputted from the lowpass filter, for example, by selectively extracting the detection signal of the sensor for recording new data, thus making it possible to control accurately the intensity of light emitted from the photoirradiation device.
In one aspect of the present invention, the photoirradiation device included in the data recording apparatus applies the light, which is lower in intensity than the light emitted when new data is recorded in the data recording medium, for erasing data recorded in the data recording medium.
In one aspect of the present invention, the apparatus is further provided with a band switching device for switching the filter band of the lowpass filter according to the data recording rate to record the data for the data recording medium.
In this case, the filter band of the lowpass filter is switched in accordance with the data recording rate, and therefore a very suitable output signal outputted from lowpass filter can be obtained even if the recording rate is changed, thus making it possible to accurately control the intensity of light emitted from the photoirradiation device.
The above object of present invention can be achieved by a data recording apparatus of the present invention. The apparatus is provided with: a photoirradiation device for applying light to a data recording medium to record data; a detection device for detecting the intensity of light emitted from the photoirradiation device; a lowpass filter for receiving a signal which is outputted from the detection device; a sampling device for sampling a signal which is outputted from the lowpass filter; a control device for controlling the intensity of light emitted from the photoirradiation device based on the signal sampled by the sampling device; and a band switching device for switching the filter band of the lowpass filter according to the data recording rate to record the data for the data recording medium.
According to this data recording apparatus, the filter band of the lowpass filter is switched according to the data recording rate in the data recording medium, and therefore an appropriate output signal outputted from the lowpass filter can always be obtained even if the recording rate varies, thus making it possible to control accurately the intensity of light emitted from the photoirradiation device.
Also, according to this data recording apparatus, circuits for peak-holding and the like are not required, and therefore the scale of the circuit can be reduced, thus making it possible to reduce the costs associated with assembling the device.
The above object of present invention can be achieved by a data recording apparatus of the present invention. The apparatus is provided with: a photoirradiation device for applying light to a data recording medium to record data; a detection device for detecting the intensity of light emitted from the photoirradiation device; a lowpass filter for receiving a signal which is outputted from the detection device; a sampling device for sampling a signal which is outputted from the lowpass filter; a control device for controlling the intensity of light emitted from the photoirradiation device based on the signal sampled by the sampling device; and a sampling timing switching device for switching the sampling timing of the sampling device according to the data recording rate to record the data for the data recording medium.
According to this data recording apparatus, the sampling timing of sampling device is switched according to the data recording rate to record the data for the data recording medium, and therefore the output signal outputted from the lowpass filter can appropriately be sample at all time even if the recording rate varies, thus making it possible to control accurately the intensity of light emitted from the photoirradiation device. Also, according to this data recording apparatus, circuits for peak-holding and the like are not required, and therefore the scale of the circuit can be reduced, thus making it possible to reduce the costs associated with assembling the device.
In one aspect of the present invention, the apparatus is further provided with a band switching device for switching the filter band of the lowpass filter according to the data recording rate to record the data for the data recording medium.
In this case, the sampling timing of sampling device is switched in accordance with the filter band of the lowpass filter, whereby the output signal outputted from the lowpass filter can be sampled in a low-waviness area.
In one aspect of the present invention, the sampling device included in the data recording apparatus samples the signal which is outputted from the lowpass filter at a point of time before the signal which is outputted from the lowpass filter converges to a predetermined level.
In this case, the output signal outputted from the lowpass filter can be sampled in the low-waviness area included in the output signal outputted from the lowpass filter, and therefore the output signal outputted from the lowpass filter can be accurately sampled, thus making it possible to accurately control the intensity of light emitted from the photoirradiation device.